Common to all lithographic systems is the presence of oil accepting and oil repelling regions. In preparing such systems, a light sensitive element is rendered oil accepting and a substrate material oil repelling.
Conventional lithographic substrates are grained, anodized (or otherwise oxidized) aluminum. Any of a variety of substances, e.g. diazo type compounds, designed to respond to actinic radiation may be applied to form a layer. The desired pattern of radiation is then projected onto the photosensitive layer (such as a layer of polymeric material) to induce a reduction in solubility of the exposed areas of the layer. Such exposed areas become oleophilic. Subsequent removal of the soluble material, i.e. the unexposed areas of the layer, reveals the hydrophilic substrate onto which the layer was originally applied. The hydrophilic substrate is not receptive to oil compatible ink.
Boutle, et al., U.S. Pat. No. 3,620,812 discloses a film material for lithographic plates which comprises a support base of polyester film material, at least one surface of which has been treated with a solution or dispersion in a volatile medium of at least one substance selected from halogen-containing phenolic substances and chlorosubstituted aliphatic acids, at a temperature of at least 30.degree. C., there being adherent to the surface so treated an interlayer such as vinyl chloride-vinyl acetate copolymers or partially hydrolyzed vinyl chloride-vinyl acetate copolymers, and there being superimposed on said interlayer a hydrophilic layer which comprises a water-swellable organic film-forming material which has been insolubilized and which contains finely divided discreet particles of an inorganic filler or fillers.
Harper, U.S. Pat. No. 4,089,687, discloses a Photographic method for printing a particle pattern which comprises applying to a supporting surface a coating composition comprising a water-soluble polymer crosslinkable into insoluble form by actinic radiation in the presence of hexavalent chromium ions, a soluble dichromate photosensitizer, a water-soluble vanadate and particles of the pattern material, exposing the coating to an actinic radiation until exposed portions of the coating are rendered insoluble, and flushing the coating with an aqueous solvent to remove soluble portions of the coating. Harper differs from the present invention in many ways. For example, the coating composition in Harper requires a water-soluble dichromate photosensitizer and a water soluble vanadate. These ingredients are not needed in the composition of the present invention. Furthermore, the method of the present invention does not require exposure to actinic radition as required by Harper.
Japanese Publications Nos. 61,044,697 (1697) and 61,148,097 ('097) disclose printing plates for producing prints. In 1697, a water-resistant support is coated with a composition comprising inorganic pigment, water soluble binder, water resistant agent and NH.sub.3 Cl that has been pH-adjusted, and then dried. The disclosure requires NH.sub.3 Cl in the composition and does not disclose crosslinking and drying techniques which are used in the present invention. In 1097, a water-resistent support is coated with a composition comprising inorganic pigments, water-soluble binders and water-resisting agents and then overcoated with a solution obtained by dissolving a metal compound which reacts with hydrophilizing solutions comprising hexacyamo metallic acid salts and/or ammonium phosphates to form hydrophilic, water-insoluble precipitates. The disclosure requires overcoating with a hexacyano metallic acid and/or ammonium phosphate solution, which is not required by the present invention.
It is desirable to have a hydrophilic, abrasion resistant and irregular surface to which a light sensitive element may effectively attach. Surface irregularities, however, must not be so coarse so as to detract from the inherent optical resolution capabilities of either the image source or the photosensitive layer.
Using the polyvinyl alcohol-pigment system of the present invention, a non-white image applied by ink jet or other such electronically controlled device absorbs radiant energy to a greater degree than a white reflective background. Heat generated in the image areas causes thermal dehydration of the PVA, rendering it oil receptive. The PVA-pigment coating system may also be used for conventional diazo-type "wipe-on" coatings. Thus, the surface is versatile in that it can be used in either a direct-to-plate computer generated imaging system or for standard wipe-on methods.
It is an object of the present invention to provide a substrate surface which is uniformly ink repelling and water compatible, wherein ink compatible regions are created by an image forming process. It is also an object of the present invention to provide a surface which is uniformly ink repelling and water compatible, wherein the surface is coated with a substance designed to be insolubilized by radiant energy. It is also an object of the invention to provide a surface which is uniformly ink repelling and water compatible, wherein an ink-jet type imaging system causes chemical modification of the PVA component of the surface rendering it hydrophobic or ink accepting. These and other objects will be described in detail in the present patent application.